For laying pipelines consisting of relatively large, heavy pipes, in particular of rigid type, it is known to use specific machines, known as pipe laying machines.
Pipe laying machines are known comprising, essentially, a frame with an internal combustion engine mounted on crawler tracks, a track guide carriage of which carries, hinged to its outside on a horizontal axis parallel to the longitudinal axis of the machine, the lower end of an arm arranged to swing in a vertical plane transversely to the machine, under the control of a respective motorized winch.
At the other end of the arm there is a lifting hook suspended from a cable which slides vertically under the control of another motorized winch, this also being supported by the frame.
On that side of the frame distant from that occupied by said arm, known machines sometimes present a counterweight which is hinged to the outside of the frame and of the respective track guide carriage by an articulated quadrilateral system controlled by an operating cylinder-piston unit.
Such known pipe laying machines have proved unsatisfactory because of their overall size.
In this respect, to transfer the machine from one operating position to another, typically by a bascule truck, the said arm has to be positioned almost vertically, which involves considerable complications seeing that when in said transporting configuration its upper end well exceeds the allowable limits for road transport.
Other dimensional drawbacks derive from the fact that the arm and any counterweight are hinged to the outside of the track guide carriage, i.e. beyond the transverse outline of the track-mounted frame.
Pipe laying machines also comprising a track-mounted frame with an internal combustion engine and a swinging arm with a lifting hook are known, in which the arm is supported by the frame by way of an interposed platform mounted on a thrust bearing.
Specifically, the base of the arm is hinged to said platform on a horizontal axis, the platform carrying at least one cylinder-piston unit for operating the swinging arm, a motorized winch for operating the hook, and a balancing weight situated on that side of the platform distant from the side occupied by said arm, and is arranged to slide between a position close to and a position distant from the platform.
By virtue of said thrust bearing device the swinging arm of such pipe laying machines has better manoeuvrability than the arm of the aforesaid pipe laying machines, and during machine transportation it can be advantageously orientated along the machine longitudinal axis in a flat position so that it lies within the allowable vertical dimension for road transport.
A problem inherent in such known machines derives from the fact that the entire load carried by the hook acts on the thrust bearing device, which means that it has to be dimensioned correspondingly, giving rise not only to cost problems but also to problems of reliability and durability.
The main object of this invention is to overcome the aforestated problems.
Another object of the invention is to attain this objective within the context of a simple, rational, low-cost, reliable and durable construction.